Stabilization of silicone fluids



. 3,309,312 .Qfi

Patented Mar. 14, 1967 3,309,312 STABILIZATION OF SlLlCONE FLUIDS Fritz A. Bnehler, Erlton, N.J., assignor to Mobil Oil Corporation, a corporation of New York No Drawing. Filed Italy 14, 1965, Ser. No. 472,010 12 Claims. (Cl. 252-18) This invention relates to stable fluid compositions and more particularly to silicone fluid compositions capable of withstanding high temperatures.

Silicone fluids have achieved wide acceptance as lubricants and hydraulic fluids which function effectively under conditions requiring high-temperature stability. At elevated temperatures, for example in the range of about 350 to about 450 F., mineral oils or synthetic lubricants become unduly viscous or even deteriorate during extended use. Silicone fluids have been found to be a satisfactory substitute. More recently, however, with the advent of engines and other machinery operating at relatively higher temperatures than before even these silicones have shown evidence of failure. At temperatures of about 600 F. and above, silicone fluids tend to gel or solidify in so short a time that the useful life of lubricants prepared from these fluids has been undesirably decreased.

Hitherto, it has been attempted to improve the service life of silicone-based lubricants and hydraulic fluids by admixing therewith certain additives which prevent or at least delay gel formation. Of these additives, iron compounds, such as iron oxide, iron octoate, and iron salts of other carboxylic acids, as described in US. Patent No. 2,445,567, have been used with some success. Unfortunately, with the ever-increasing demand for functional lubricants and fluids to operate for long periods of time at such extreme temperatures, it has been found that the stabilization obtained from the use of these iron compounds alone is not always sutficient and further improvement in the stability of silicone fluids would be highly desirable.

The major object of the present invention is to provide silicone fluids having extended service life at high temperatures. A further object is to provide silicone fluids containing iron compounds, having improved high temperature stability. These and other objects will become apparent from the following description.

It has now been discovered that the high temperature stability of silicone fluids may be unexpectedly increased by adding thereto a minor amount of an iron compound and an amino acid which has the formula Ht-NR'C-0ii wherein R may be alkyl, cycloalkyl, aralkyl, aryl, and aikaryl having from 1 to about 20 carbon atoms. R may also have other substituents, namely hydroxy, sulfhydryl, thio and additional amino groups.

The silicone fluids which are used in the practice of this invention are polysiloxanes having as its repeating unit the formula n L-n/Z wherein n is in the range of from about 1.1 to about 2.9 and R is an alkyl or aryl radical, which terms cover cycloalkyl, alkaryl, and aralkyl radicals. R also includes substituted radicals containing halogen, oxygen and nitrogen atoms attached thereto, such as halogenated hydrocarbon groups, ether groups, carboxylate groups, ester groups, and cyanoalkyl groups. In general, R contains from 1 to about 20 carbon atoms. Included in the above definition are methyl, propyl, pentyl, hexyl, decyl, and the like as examples of alkyl groups; cyclo-hexyl, cyciopentyl and the like as examples of cycloalkyl groups; and phenyl, naphthyl, benzyl, tolyl, xylyl and the like as examples of the various aromatic groups. Also included are mixed groups in which R may be both alkyl and aryl in the same molecule. Of special interest in this invention are polysiloxane fluids wherein the R group contains (1) alkyl radicals; (2) mixed alkyl and aryl radicals wherein the mol ratio of alkyl to aryl is in the range of from 1 to about 15 to 1; or (3) mixed alkyl, aryl, and haloaryl radicals wherein the mol ratio of alkyl to the total aryl and haloaryl is from 1 to about 15 to 1, and the said haloaryl radicals contain from 1 to 5 halogen atoms each. Instead of the above groups being mixed in the same molecule, polysiloxanes containing one or more of the R groups of (1), (2) and (3) above in physical mixture are also within the scope of this invention.

The molecular weights of these silicone fluids vary depending upon the method of preparation and the reactants used in their preparation. Broadly, these fluids may possess molecular weights fro-m about 200, and more frequently from about 500, to about 10,000.

Polysiloxanes of the type used in the present invention are well known to the art. Their preparation and purpose are disclosed in Introduction to the Chemistry of the Siiico-nes, E. G. Rochow, Second Edition (1951) lohn Wiley & Sons, New York, and Organo Silicon as Compounds, C. Eaborne (1960), Academic Trust, New York.

These polysiloxane fluids (also termed silicone fluids for the purpose of this invention), contain, as a first additive stabilizer, an iron compound, such as iron oxide, and preferably the iron salts of organic acids. The organic acids used to prepare the iron compound stabilizers are carboxylic acids which may be saturated or unsaturated; aliphatic, cycloaliphatic or aromatic acids. Included in this category are acetic, propionic, butyric, 2- ethylhexanoic (octoic), benzoic, toluic, cyclohexanoic, and other iron salts disclosed in US. Patent No. 2,445,- 5 67. Of primary interest in this invention is iron octoate.

The second additive which provides the increased stabilization of the polysiloxane fluids, as described above, are amino mono-carboxylic acids having the formula wherein R may be an aliphatic or aromatic radical having u to about 20 carbon atoms. The most preferred acids are the alpha-amino acids, including the two simplest acids of each R-type: glycine, wherein R is methylene, and anthranilic, wherein R is an o-phenylene. Other-suitable acids include those of the hydroxyamino acid class and the sulfur-substituted amino acid class. Acids such as alanine, cysteine, serine and paminobenzoic acid are included in the defined group of acids in this invention.

The amount of iron compound to be added to the silicone fluids of this invention is in the range of about 0.001% to about 10% by weight. These iron compounds are so effective that as little as about 0.001% to about 0.75% furnish significant results in extending the service life of these fluids. With regard to the amino mono-carboxylic acid, amounts ranging from about 0.1% to about 10%, and preferably about 0.5% to about 5%, by weight of the total composition are employed.

The following examples are intended to illustrate the instant invention without introducing limitations theretO.

EVALUATION OF SILICONE COMPOSITIONS The high temperature stability of the silicone compositions of this invention is measured by subjecting the fluid composition to 600 F. temperature in the presence of air and by determining the time at which the composition gels or commences to turn solid. The test procedure is as follows:

A sample of the silicone fluid composition is added to a Pyrex beaker and is placed in an oven held at 600 F. under forced air circulation. The fluidity of the compositions is checked visually at regular intervals until the sample shows no gravity flow. The time elapsed from the beginning of the test to this point is denoted as the gel time of the sample.

The compositions in these examples may be prepared by any simple mixing means using any desired sequence of addition.

Example I The silicone fluid used in this example is a methyl phenyl polysiloxane having a methyl to phenol mol ratio of 8:1, a molecular weight of about 3000 and a kinematic viscosity at 210 F. of 20 centistokes. To two portions of the silicone fluid were added varying quantities of iron octoate and both iron octoate and glycine in a combined composition. The high temperature gel test was applied to the uninhibited silicone fluid and to the two inhibited compositions. The results are tabulated below The silicone fluid of Example I was combined with 0.2% by Weight of iron octoate and 1.0% by weight of anthranilic acid. The high temperature stability test was applied to these compositions with the following results tabulated in Table II.

TABLE II Wt. Gel Additive Percent Time,

Hrs.

1. None. 2. Iron Octoate 0.2 550 3. Anthranilic acid/iron octoate 1. 0/0 2 1, 100

It will be noted from the results of the gel test in the above examples that the amino mono-carboxylic acids, when used in combination with iron containing stabilizers are effective in improving the high temperature stability of silicone fluids.

The stabilized silicone compositions of this invention may be employed as lubricants, whether alone or in admixture with petroleum oils or synthetic oils, and as hydraulic fluids in many industrial applications. The silicone fluid compositions of this invention may also contain other known additives including detergents, rust inhibitors, viscosity improving agents, and extreme pressure agents.

These fluids may also be thickened into lubricating greases by the addition of known pigment thickeners. Chief among these are the perylimids which have the structure wherein R and R may he hydrogen, alkyl, aryl, alkaryl, and halogen derivatives thereof, and may be alike or different. Other suitable thickeners are the anthanthrones:

wherein R and R are the same or different, being halogen, alkyl, aryl, alkoxy, and halogen derivatives thereof. Also suitable are azoles, naphthalic imidazoles, Milori blues (terrocyanides), indanthrene blue pigment or vat dye, polyaryl ureas, ammeline and hydrophobic clays. One or several of these thickeners may be used together and they may represent about 5% to 75% by weight, and preferably about 15% to 30%, of the total composition. The remainder of the grease composition is the silicone and sulfur-containing substance of this invention.

The present invention has been described and illustrated by reference to certain specific examples without intending to limit the invention in any way thereto; and modifications may be employed without departing from the scope of this invention thereby, except as indicated in the following-claims.

I claim:

1. A high temperature stabilized composition comprising a major proportion of a polysiloxane fluid having the unit formula:

wherein n has a value from about 1.1 to about 2.9 and R represents an organyl radical selected from the group consisting of alkyl and aromatic radicals and halogenated derivatives thereof R containing from 1 to about 20 carbon atoms and a minor proportion suflicient to stabilize said fluid of (1) an iron compound selected from the group consisting of iron oxide and iron carboxylate salts soluble in said polysiloxane fluid and (2) an amino mono-carboxylic acid.

2. A high temperature stabilized fluid composition comprising a major proportion of a polysiloxane fluid having the unit formula:

wherein n has a value from about 1.1 to about 2.9 and R represents an organyl radical selected from the group consisting of alkyl, cycloalkyl, aralkyl R containing from 1 to about 20 carbon atoms, aryl, and alkaryl, and halogenated derivatives thereof and a minor proportion sumcient to stabilize said fluid of (1) an iron compound selected from the group consisting of iron oxide and an iron 0 salt of a carboxylic acid soluble in said polysiloxane fluid wherein R is selected from the group consisting of alkyl, cycloalkyl, aralkyl, aryl and alkaryl having from 1 to about 20 carbon atoms.

3. The fluid composition of claim 2 wherein the aminomonocarboxylic acid is an alpha-amino acid.

4. The fluid composition of claim 3 wherein the alphaamino acid is glycine.

5. The fluid composition of claim 3 wherein the alphaamino acid is anthranilic acid.

6. The high temperature stabilized fluid composition comprising a major proportion of a polysiloxanc fluid having the unit formula:

wherein n has a value from 1.1 to 2.9 and R is selected from the group consisting of (a) alkyl radicals, (b) mixed alkyl and aryl radicals in a mol ratio of alkyl to aryl of from 1 to about 15, (c) mixed alkyl and halogenated aryl radicals in a mol ratio of alkyl to halogenated aryl of from 1 to about 15 and (d) mixed alkyl, aryl and halog-enated aryl radicals in a mol ratio of alkyl to total aryl and halogenated aryl of from 1 to about 15 said halogenated aryl radicals in all instances containing from 1 to 5 halogen atoms each R containing from 1 to about 20 carbon atoms, and a minor proportion sufficient to stabilize said fluid of (1) from about 0.001% to about 10% by weight of a soluble iron salt of a carboxylic acid selected from the group consisting of aliphatic, cyclo-aliphatic, and aromatic carboxylic acids and (2) from about 0.1% to about 10% by weight of an amino mono-carboxylic acid having a formula II HrN-IV-C-OH wherein R is selected from the group consisting of alkyl, cycloalkyl, aralkyl, aryl and alkaryl having from 1 to about 20 carbon atoms.

7. The fluid composition of claim 6 wherein from about 0.001% to about 0.75% by weight of said iron salt is present.

8. The fluid composition of claim 6 wherein from about 0.5 to about 5% by weight of the said amino mono-carboxylic acid is present.

9. The fluid composition of claim 6 wherein the iron salt is iron octoate.

10. The fluid composition of claim 6 wherein the amino mono-carboxylic acid is an alpha-amino acid.

11. The fluid composition of claim 10 wherein the alpha-amino acid is glycine.

12. The fluid composition of claim 10 wherein the alpha-amino acid is anthranilic acid.

References Cited by the Examiner UNITED STATES PATENTS DANIEL E. WY MAN, Primary Examiner.

C. F. DEES, Assistant Examiner. 

1. A HIGH TEMPERATURE STABILIZED COMPOSITION COMPRISING A MAJOR PORTION OF A POLYSILOXANE FLUID HAVING THE UNIT FORMULA: 